HK1172603A - Low dielectric glass and fiber glass for electronic applications - Google Patents

Description

Low dielectric glass and glass fibers for electronic applications

The present application is a divisional application of an invention patent application having an application date of 24/10/2007, an application number of 200780046066.2, and an invention name of "low dielectric glass and glass fiber for electronic applications".

Technical Field

The present invention relates to glass compositions suitable for forming fibers useful for reinforcing composite substrates comprising printed circuit boards ("PCBs"). In more detail, the invention relates to glass fiber reinforced materials with electrical properties that allow to enhance the performance of PCBs.

Background

“D_k"is the dielectric constant, also called" permittivity ", of a material and is a measure of the ability of the material to store electrical energy. The material to be used as a capacitor desirably has a relatively high D_kWhile materials to be used as part of a PCB substrate are desired to have a low D_kParticularly for high speed circuits. D_kIs the ratio of the charge that a given material can store between two metal plates (i.e., the capacitance) to the amount of charge that the gap between the same two metal plates (air or vacuum) can store. "D_f"or loss tangent is a measure of the electrical energy loss of a dielectric material. D_fIs the ratio of the resistive loss component of the current to the capacitive component of the current and is equal to the tangent of the loss angle. For high speed circuits, D containing the material of the PCB substrate is desirable_fIs relatively low.

PCBs are typically reinforced with glass fibers of the "E glass" family of various compositions, based on the "glass fiber yarn standard specification" D578 american society for testing and materials. According to this specification, E-glass for electronic applications contains 5 to 10% by weight of B₂O₃This reflects to B₂O₃Knowledge of the desired effect on the dielectric properties of a glass composition. E-glass fibers for electronic applications typically have a D of 6.7-7.3 at a frequency of 1MHz_k. Standard electronic E-glass is also formulated to provide melting and forming temperatures that allow practical manufacturing. The forming temperature (temperature at which the viscosity is 1000 poise), also referred to herein as T, for commercial electronic E-glass_FAnd is usually 1170 ℃ to 1250 ℃.

For applications in communications and electronic computing, high performance printed circuit boards need to have a lower D compared to E-glass for better performance, i.e. less noise signal transmission_kThe substrate reinforcing material of (1). Optionally, the electronics industry also desires to reduce D relative to E-glass_f. While the PCB industry has a need for low dielectric glass fibers, the manufacture of glass fiber reinforcements requires solutions to economic durability issues in order for low dielectric fibers to be successfully commercialized. To this end, some of the disadvantages proposed in the prior artD_kThe glass composition does not adequately address the economic problem.

Some low dielectric glasses in the prior art are characterized by high SiO₂High content or high B₂O₃Content of, or high SiO₂And high B₂O3_{Is/are as follows}And (4) combining. An example of the latter is referred to as "D glass". Such low D can be found in the article "Dielectric Properties of glass series Ultra-High frequency and the Relation relationship" of L.Navias and R.L.Green, "J.Am.Ceram.Soc., 29, 267-276(1946), in U.S. patent application 2003/0054936A1(S.Tamura), and in patent application JP 3409806B2(Y.Hirokazu)_kDetails of the glass acquisition process. SiO 2₂And D glass type glass fibers are used as reinforcement in the form of fibers in PCB substrates such as laminates of woven fibers and epoxy resins. Although these approaches all successfully provide low D, sometimes as low as about 3.8 or 4.3_kHowever, the high melting and forming temperatures of these compositions result in undesirably high costs for these fibers. D-glass fibers typically require a forming temperature, SiO, in excess of 1400 deg.C₂The fibers require a forming temperature of about 2000 ℃. In addition, the D glass is characterized by B of up to 20 weight percent or more₂O₃And (4) content. Because B₂O₃Is one of the most expensive raw materials required to manufacture conventional electronic E glass, and a large amount of B is contained in D glass compared with E glass₂O₃The use of (a) significantly increases its cost. Thus, SiO₂And D glass fibers do not provide a practical solution for large-scale manufacturing of high-performance PCB substrate materials.

JP 3409806B2(Hirokazu) describes a high B-based solution₂O₃Other low dielectric glass fibers at levels (i.e., 11-25 wt.%) plus other relatively high cost components such as ZnO (up to 10 wt.%) and BaO (up to 10 wt.%), report D_kThe value is 4.8-5.6 at 1 MHz. The inclusion of BaO in these compositions is problematic for cost as well as environmental reasons. Despite the high cost of B in the compositions of this reference₂O₃In an amount ofHigh, the disclosed fiber forming temperatures are still relatively high, e.g., 1355 ℃ to 1429 ℃. Similarly, U.S. patent application 2003/0054936A1(Tamura) describes high B based₂O₃Concentration (i.e. 14-20 wt.%) coupled with relatively high cost of TiO₂(up to 5% by weight) of other low dielectric glasses at 1MHz_k4.6-4.8 and loss factor D_f0.0007-0.001. Japanese patent application JP02154843A (Hiroshi et al) discloses D at 1MHz_k5.2 to 5.3 of boron-free low dielectric glass. Although these boron-free glasses provide low D at potentially relatively low raw material costs_kHowever, they have the disadvantage that the fiber-forming temperature at a melt viscosity of 1000 poise is high, 1376 ℃ to 1548 ℃. In addition, these boron-free glasses have a very narrow forming window (the difference between the forming temperature and the liquidus temperature), typically 25 ℃ or less (negative in some cases), while a window of about 55 ℃ or higher is generally considered suitable in the commercial glass fiber industry.

In order to improve PCB performance while controlling the increase in cost, it may be advantageous to provide compositions for glass fibers that impart significantly improved electrical properties relative to E-glass compositions (D)_kAnd/or D_f) And simultaneously with SiO₂Lower actual forming temperatures than the D glass type and other prior art methods of obtaining the low dielectric glass described above. In order to significantly reduce raw material costs, it is necessary to maintain B₂O₃Less than D glass, e.g., less than 13 weight percent or less than 12 weight percent, and in some cases the glass composition may also advantageously fall within ASTM specifications for electronic E glass, and thus not more than 10 weight percent B is required₂O₃. Low D can also be advantageously produced_kGlass fibers do not require expensive materials such as BaO or ZnO that are not conventional in the glass fiber industry. Additionally, commercially useful glass compositions require tolerance for impurities in the raw materials, which also allows for the use of less costly batch materials.

Since the important role of the glass fibers in the PCB composite is to provide mechanical strength, it is desirable to obtain improvements in electrical performance without significantly sacrificing glass fiber strength. Glass fiber strength can be expressed in terms of young's modulus or green tensile strength. It would also be desirable to manufacture PCBs without requiring major changes in the resins used or at least substantially without requiring higher cost resins if new low dielectric glass fiber solutions are to be used, as would be required by some alternative approaches.

Disclosure of Invention

The fiberizable glass compositions of the present invention provide improved electrical properties (i.e., low D) relative to standard E-glass_kAnd/or low D_f) While providing a lower D than the prior art_kThe glass scheme is more feasible for forming fibers for commercial applications in temperature-viscosity relationships. Another optional aspect of the invention is that at least some of the compositions can be commercially manufactured at relatively low raw material batch cost. In one aspect of the invention, the glass composition comprises the following components, which may be in the form of glass fibers:

SiO₂60-68 wt%;

B₂O₃7-13 wt%;

Al₂O₃9-15 wt%;

8-15 wt% of MgO;

0-4 wt% of CaO;

Li₂0-2 wt% of O;

Na₂0-1 wt% of O;

K₂0-1 wt% of O;

Fe₂O₃0-1 wt%;

F₂0-1 wt%;

TiO₂0 to 2% by weight.

In some embodiments, the compositions of the present invention are characterized by a relatively low CaO content, for example, from about 0 to 4 weight percent. In another embodiment, the CaO content can be from about 0 to about 3 weight percent. In general, minimizing the CaO content yields improvements in electrical properties, and in some embodiments reducing the CaO content to such a low level that it can be considered an optional ingredient. On the other hand, the MgO content of this type of glass is relatively high, with in some embodiments twice the CaO content (on a weight percent basis). Some embodiments of the invention may have a MgO content of greater than about 6.0 wt.%, while in other embodiments, the MgO content may be greater than 7.0 wt.%.

As noted above, some of the low D's of the prior art_kThe composition has the disadvantage of requiring the inclusion of a large amount of BaO, and it can be noted that BaO is not required in the glass composition of the present invention. While the advantageous electrical and manufacturing properties of the present invention do not preclude the presence of BaO, the absence of intentionally included BaO is considered an additional advantage of some embodiments of the present invention. Accordingly, embodiments of the present invention are characterized by the presence of less than 1.0 wt.% BaO. In those embodiments where only trace impurities are present, the BaO content can be expressed as no greater than 0.05 wt.%.

The compositions of the present invention contain a lower amount of B than prior art processes₂O₃Said prior art method relies on a high B₂O₃To realize low D_k. This results in significant cost savings. In some embodiments, B is required₂O₃Not greater than 13 wt%, or not greater than 12 wt%. Some embodiments of the present invention also fall within the ASTM specifications for electronic E-glass, i.e., no greater than 10 weight percent of B₂O₃。

In the compositions given above, the ingredients are proportioned so as to obtain a glass having a lower dielectric constant than standard E-glass. With respect to standard electronic E-glass for comparison, this may be less than about 6.7 at a frequency of 1 MHz. In other embodiments, the dielectric constant (D) is at a frequency of 1MHz_k) Can be used forTo be less than 6. In other embodiments, the dielectric constant (D) is at a frequency of 1MHz_k) May be less than 5.8. Further embodiments exhibit a dielectric constant (D) of less than 5.6 or even less at a frequency of 1MHz_k)。

The compositions given above have the desired temperature-viscosity relationship that is feasible for practical commercial manufacture of glass fibers. Generally, lower temperatures are required to make fibers than prior art type D glass compositions. The desired properties can be expressed in many ways and they can be obtained by the compositions of the invention, alone or in combination. Generally, glass compositions within the ranges given above can be made that exhibit a forming temperature (T) of no greater than 1370 ℃ at a viscosity of 1000 poise_F). T in some embodiments_FNot greater than 1320 ℃, or not greater than 1300 ℃, or not greater than 1290 ℃. These compositions also encompass compositions wherein the forming temperature and liquidus temperature (T)_L) Glasses with a positive difference between them, in some embodiments, a forming temperature at least 55 ℃ above the liquidus temperature, are advantageous for commercial manufacture of fibers from these glass compositions.

In general, minimizing the alkali metal oxide content of the glass composition helps to reduce D_k. In which it is necessary to make D_kIn those embodiments in which the reduction is optimized, the total alkali metal oxide content is no greater than 2 weight percent of the glass composition. It has been found in the compositions of the present invention that Na is added in this regard₂O and K₂O minimization ratio Li₂O is more effective. The presence of alkali metal oxides generally results in lower forming temperatures. Thus, in those embodiments of the invention that preferentially provide relatively low forming temperatures, a substantial amount of Li is included₂O, for example at least 0.4 wt%. To this end, in some embodiments, Li₂O content greater than Na₂O or K₂The content of O, in other embodiments, Li₂O content greater than Na₂O and K₂The sum of the O content is, in some embodiments, two times or more.

In addition to or instead ofIn lieu of the features of the invention described hereinabove, the compositions of the invention can be used to provide lower loss tangent (D) than standard electronic E-glass_f) The glass of (2). In some embodiments, D is at 1GHz_fNot greater than 0.0150, and in other embodiments, not greater than 0.0100 at 1 GHz.

One advantageous aspect of the invention in some embodiments relies on components that are conventional in the glass fiber industry and avoids large quantities of components whose raw material sources are costly. For this aspect of the invention, components other than those explicitly set forth in the compositional definition of the glasses of the invention may be included in a total amount of no greater than 5 weight percent, although not required. These optional components include melting aids, fining aids, colorants, trace impurities, and other additives known to those skilled in the art of glass making. Low D relative to some prior art_kGlass, BaO is not required in the compositions of the present invention, but inclusion of small amounts of BaO (e.g., up to about 1 wt%) may not be excluded. Also, a large amount of ZnO is not required in the present invention, but may be included in small amounts (e.g., up to about 2.0 wt%) in some embodiments. In those embodiments of the invention where optional components are minimized, the sum of the optional components is no greater than 2 wt.%, or no greater than 1 wt.%. In other words, it can be said that some embodiments of the present invention consist essentially of the enumerated components.

Detailed Description

For lower D_kAnd D_fComprising SiO with a low electric susceptibility₂And B₂O₃Are effective in the compositions of the present invention. Although B is₂O₃It melts at low temperatures (350 ℃) but is unstable to moisture attack in ambient air and therefore pure B₂O₃Fibers are not feasible for use in PCB laminates. SiO 2₂And B₂O₃Both network formers, the mixture of which can lead to significantly higher fiber forming temperatures than E-glass, and for D-glass. MgO and Al may be included for lower fiber forming temperature₂O₃Instead of some SiO₂. Calcium oxide (CaO) and SrO may also be used in combination with MgO, although they are less desirable than MgO because they both have a higher polarizability than MgO.

To reduce batch cost, B is used at a lower level than in D glass₂O₃. However, sufficient B is contained₂O₃To prevent phase separation in the glass melt and thereby provide better mechanical properties to glass fibers made from the composition.

The choice of batch ingredients and their cost depend significantly on their purity requirements. Typical commercial ingredients (e.g. for E-glass manufacture) contain Na₂O、K₂O、Fe₂O₃Or FeO, SrO, F₂、TiO₂、SO₃And the like in various chemical forms. Most of the cations from these impurities pass through the SiO in the glass₂And/or B₂O₃Non-bridging oxygen is formed to increase the D of the glass_k。

Sulfates (as SO) may also be present₃Meter) as a clarifying agent. Minor impurities from the raw materials or from contamination during the melting process, e.g. SrO, BaO, Cl, may also be present₂、P₂O₅、Cr₂O₃Or NiO (not limited to these particular chemical forms). Other fining agents and/or processing aids such As As may also be present₂O₃、MnO、MnO₂、Sb₂O₃Or SnO₂(not limited to these particular chemical forms). Each of these impurities and fining agents, when present, are typically present in an amount less than 0.5 wt.% of the total glass composition. Optionally, elements of the rare earth group of the periodic table of the elements, including atomic numbers 21(Sc), 39(Y), and 57(La) to 71(Lu), may be added to the compositions of the present invention. These elements can act as processing aids or improve the electrical, physical (thermal and optical), mechanical and chemical properties of the glass. These rare earth additives may be included in the original chemical form and in the oxidized state. It is considered that the addition of the rare earth element isOptionally, especially in those embodiments of the invention having the goal of minimizing raw material costs, as they increase the cost of the batch even at low concentrations. Regardless, their cost generally requires that the rare earth components (measured as oxides), when present, be present in an amount no greater than about 0.1-1.0 wt.% of the total glass composition.

The invention will be described by the following series of specific embodiments, however, it will be appreciated by those skilled in the art that many other embodiments are contemplated in accordance with the principles of the invention.

The glasses in these examples were made by melting a mixture of reagent grade chemicals in powder form in a 10% Rh/Pt crucible for 4 hours at 1500 ℃ -1550 ℃ (2732 ° F-2822 ° F). Each batch was about 1200 grams. After a 4-hour melting period, molten glass was poured onto a steel plate for quenching. To compensate for B₂O₃Volatilization loss (typically about 5% in laboratory batch melting conditions for a 1200 gram batch size), boron retention coefficient in batch calculations was set to 95%. Other volatile species such as fluorides and alkali metal oxides are not regulated in the batch for their emission losses due to their low concentration in the glass. The compositions in the examples represent compositions in the batch state. Because reagent chemicals are used to make B with adequate regulation₂O₃The batch-state composition described in the present invention is considered to be close to the measured composition.

The melt Viscosity as a function of Temperature and Liquidus Temperature was determined by the Standard Practice for Measuring Glass Above the Softening Point using ASTM test methods C965 "Standard Practice for Measuring Glass Viscosity Above the Softening Point" and C829 "Standard Practice for Measuring Glass Liquidus Temperature by the Gradient furnace method (Standard Practice for Measuring liquid Temperature of Glass by the Gradient furnace method", respectively).

Using a respective one having a diameter of 40mm and a thickness of 1-1.5mmPolished disks (disks) of glass samples, made of annealed glass, measure electrical and mechanical properties. The Dielectric Constant (D) of each glass from 1MHz to 1GHz was determined by ASTM Test method D150 "Standard Test method for A-C Loss characteristics and Permittivity (Dielectric Constant) of Solid Electrical insulation (Standard Test Methods for A-C Loss Properties and Performance (Dielectric Constant)" (D1-C Loss characteristics and Permittivity of Solid Electrical insulation)_k) And loss factor (D)_f). According to this procedure, all samples were pretreated for 40 hours at 25 ℃ and 50% humidity. The glass Density was selectively tested using ASTM Test Method C729 "Standard Test Method for glass Density by Sink-Float Comparator" for which all samples were annealed.

For selected compositions, the microindentation method was used to determine the young's modulus (from the initial slope of the indentation load-indentation depth curve in the indenter unloading cycle) and microhardness (from the maximum indentation load and the maximum indentation depth). For the test, use is made of_kAnd D_fThe same disc samples were tested. 5 press-in measurements were performed to obtain average young's modulus and microhardness data. The micro-intrusion device was calibrated using a commercial reference glass block having a product name of BK 7. The reference glass had a Young's modulus of 90.1GPa with a standard deviation of 0.26GPa and a microhardness of 4.1GPa with a standard deviation of 0.02GPa, which were both based on 5 measurements.

All compositional values in the examples are in weight percent.

TABLE 1 compositions

Examples 1-8 provide glass compositions in weight percent (table 1): SiO 2₂ 62.5-67.5％、B₂O₃ 8.4-9.4％、Al₂O₃ 10.3-16.0％、MgO 6.5-11.1％、CaO 1.5-5.2％、Li₂O 1.0％、Na₂O 0.0％、K₂O 0.8％、Fe₂O₃ 0.2-0.8％、F₂ 0.0％、TiO₂0.0% and sulfate (in)SO₃Calculated) 0.0 percent.

The glass was found to have a D of 5.44 to 5.67 at a frequency of 1MHz_kAnd D of 0.0006 to 0.0031_fAnd D having a frequency of 5.47-6.67 at 1GHz_kAnd D of 0.0048 to 0.0077_f. The electrical properties of the compositions in series III demonstrate significantly lower (i.e., improved) D than standard E-glass_kAnd D_fSaid E-glass having a D at 1MHz of 7.29_kAnd D of 0.003_fAnd D at 1GHz of 7.14_kAnd D of 0.0168_f。

With respect to fiber forming properties, the compositions in Table 1 had a forming temperature (T) of 1300-1372 deg.C_F) And a forming window (T) of 89-222 DEG C_F-T_L). This may be in conjunction with T_FTypically 1170-1215 ℃ standard E glass. A forming window (T) greater than 55 ℃ to prevent glass devitrification during fiber forming_F-T_L) Is ideal. All compositions in table 1 exhibited satisfactory forming windows. While the compositions in table 1 have higher forming temperatures than E-glass, they have significantly lower forming temperatures than D-glass (typically about 1410 ℃).

TABLE 1

TABLE 2 compositions

Examples 9-15 provide glass compositions: SiO 2₂ 60.8-68.0％、B₂O₃8.6 and 11.0% Al₂O₃ 8.7-12.2％、MgO 9.5-12.5％、CaO 1.0-3.0％、Li₂O 0.5-1.5％、Na₂O 0.5％、K₂O 0.8％、Fe₂O₃ 0.4％、F₂ 0.3％、TiO₂0.2% and sulphate (as SO)₃Calculated) 0.0 percent.

The glass was found to have a frequency of 5.55-5.9 at 1MHz5D_kAnd D of 0.0002 to 0.0013_fAnd D at a frequency of 1GHz in the range of 5.54-5.94_kAnd D of 0.0040 to 0.0058_f. The electrical properties of the compositions in Table 2 illustrate significantly lower (i.e., improved) D than standard E-glass_kAnd D_fSaid E-glass having a D at 1MHz of 7.29_kAnd D of 0.003_fAnd D at 1GHz of 7.14_kAnd D of 0.0168_f。

With respect to mechanical properties, the compositions in Table 2 had Young's modulus of 86.5-91.5GPa and microhardness of 4.0-4.2GPa, which is equal to or higher than that of standard E-glass having Young's modulus of 85.9GPa and microhardness of 3.8 GPa. The young's modulus of the compositions in table 2 is also significantly higher than that of D-glass, which is about 55GPa based on literature data.

Regarding the fiber forming properties, and a fiber having a T of 1170-1215 ℃_FCompared to standard E glass, the compositions of Table 2 have a forming temperature (T) of 1224-_F) And a forming window (T) of 6-105 DEG C_F-T_L). Some (but not all) of the compositions of Table 2 have a forming window (T) greater than 55 ℃_F-T_L) This is considered preferable in some cases to avoid glass devitrification in commercial fiber forming operations. The forming temperatures of the compositions of Table 2 were lower than those in D glass (1410℃.), although higher than that of E glass.

TABLE 2

TABLE 3

Example (b):	16	17	18	19	20
						Al2O3	10.37	11.58	8.41	11.58	12.05
B2O3	8.71	10.93	10.66	8.98	8.69
						CaO	2.01	2.63	3.02	1.78	2.12
F2	0.32	0.30	0.30	0.30	0.30
						Fe2O3	0.40	0.27	0.27	0.27	0.27
K2O	0.79	0.25	0.25	0.16	0.10
						Li2O	0.50	1.21	1.53	0.59	1.40
MgO	11.06	10.04	9.65	11.65	10.57
						Na2O	0.52	0.25	0.57	0.35	0.15
SiO2	65.13	62.55	65.35	64.35	64.35
						TiO2	0.20	0.00	0.00	0.00	0.00
sum of	100.00	100.00	100.00	100.00	100.00
						Dk，1MHz	5.43	5.57		5.30	5.42
Dk，1GHz	5.33	5.48		5.22	5.33
						Df，1MHz	0.0057	0.0033		0.0031	0.0051
Df，1GHz	0.0003	0.0001		0.0008	0.0014
						TL(℃)	1231	1161	1196	1254	1193
TF(℃)	1327	1262	1254	1312	1299
						TF-TL(℃)	96	101	58	58	106
TM(℃)	1703	1592	1641	1634	1633
						E(GPa)	85.3	86.1	85.7	91.8	89.5
Std E(GPa)	0.4	0.6	2.5	1.7	1.5
						H(GPa)	3.99	4.00	4.03	4.22	4.13
Std H(GPa)	0.01	0.02	0.09	0.08	0.05

Table 3 (continuation)

TABLE 4

Example (b):	27	28	e glass
				Al2O3	12.42	12.57	13.98
B2O3	9.59	8.59	5.91
				CaO	0.11	0.10	22.95
F2	0.35	0.26	0.71
				Fe2O3	0.21	0.21	0.36
K2O	0.18	0.18	0.11
				Li2O	0.80	1.01	0
MgO	10.25	10.41	0.74
				Na2O	0.15	0.18	0.89
SiO2	65.47	65.96	54.15
				TiO2	0.17	0.17	0.07
Dk，1MHz	5.3	5.4	7.3
				Dk，1GHz	5.3	5.4	7.1
Df，1MHz	0.003	0.008
				Df，1GHz	0.011	0.012	0.0168
TL(℃)	1184	1201	1079
				TF(℃)	1269	1282	1173
TF-TL(℃)	85	81	94
				E(GPa)
H(GPa)	3.195	3.694

Claims (20)

1. A glass composition suitable for fiber formation comprising:

SiO₂60-68 wt%;

B₂O₃7-12 wt%;

Al₂O₃9-14 wt%;

8-14 wt% of MgO;

0-4 wt% of CaO;

Li₂0-2 wt% of O;

Na₂0-1 wt% of O;

K₂0-1 wt% of O;

Fe₂O₃0-1 wt%;

F₂0-2 wt%;

TiO₂0-2 wt%; and

0 to 5% by weight in total of the remaining components;

wherein (Li)₂O+Na₂O+K₂O) is less than 2 wt.%, and wherein the MgO content is at least twice the CaO content on a weight basis.

2. A glass composition suitable for fiber formation comprising:

B₂O₃less than 12 wt%;

Al₂O₃9-14 wt%;

8-14 wt% of MgO;

0-4 wt% of CaO;

SiO₂60-68 wt%;

Li₂0-2 wt% of O;

Na₂0-1 wt% of O;

K₂0-1 wt% of O;

Fe₂O₃0-1 wt%;

F₂0-2 wt%; and

TiO₂0-2 wt%;

wherein (Li)₂O+Na₂O+K₂O) is less than 2 wt.% and wherein the MgO content is at least twice the CaO content on a weight basis, the glass exhibiting a dielectric constant (D) of less than 6.7_k) And a forming temperature (T) of no greater than 1370 ℃ at a viscosity of 1000 poise_F)。

3. A glass composition suitable for fiber formation comprising:

SiO₂60 to 68 weight portionsAmount%;

B₂O₃7-12 wt%;

Al₂O₃9-14 wt%;

8-14 wt% of MgO;

0-3 wt% of CaO;

Li₂0-2 wt% of O;

Na₂0-1 wt% of O;

K₂0-1 wt% of O;

Fe₂O₃0-1 wt%;

F₂0-2 wt%; and

TiO₂0-2 wt%;

wherein (Li)₂O+Na₂O+K₂O) is less than 2 wt.% and wherein the MgO content is at least twice the CaO content on a weight basis, the glass exhibiting a dielectric constant (D) of less than 5.9_k) And a forming temperature (T) of not more than 1320 ℃ at a viscosity of 1000 poise_F)。

4. The composition according to any one of claims 1 or 2, wherein the CaO content is 0-3 wt%.

5. The composition of any of claims 1-3, wherein the MgO content is 8-13 wt%.

6. The composition of any of claims 1-3, wherein the MgO content is 9-12 wt%.

7. The composition of any one of claims 1-3, wherein B₂O₃The content is not more than 11 wt%.

8. The composition of any one of claims 1-3, whereinAl₂O₃The content is 10-13 wt%.

9. The composition of claim 1, wherein the components are selected to provide a dielectric constant (D) of less than 6.7 at a frequency of 1MHz_k) The glass of (2).

10. The composition of any one of claims 1 or 2, wherein the components are selected to provide a dielectric constant (D) of less than 6 at a frequency of 1MHz_k) The glass of (2).

11. The composition of any of claims 1-3, wherein the components are selected to provide a dielectric constant (D) of less than 5.8 at a frequency of 1MHz_k) The glass of (2).

12. The composition of any of claims 1-3, wherein the components are selected to provide a dielectric constant (D) of less than 5.6 at a frequency of 1MHz_k) The glass of (2).

13. The composition of claim 1, wherein the components are selected to provide a forming temperature T of no greater than 1370 ℃ at a viscosity of 1000 poise_F。

14. The composition of any one of claims 2, 3, or 13, wherein the components are selected to provide a liquidus temperature (T) at least 55 ℃ lower than the forming temperature_L)。

15. The composition of any one of claims 1 or 2, wherein the components are selected to provide a forming temperature T of no greater than 1320 ℃ at 1000 poise viscosity_F。

16. The composition of any one of claims 3 or 15, wherein the components are selected to provide a liquidus temperature (T) at least 55 ℃ lower than the forming temperature_L)。

17. A composition as claimed in any one of claims 1 to 3 wherein the composition comprises 0 to 1% by weight BaO and 0 to 2% by weight ZnO.

18. The composition of any one of claims 1-3, wherein the composition is substantially free of BaO and substantially free of ZnO.

19. A composition as claimed in any one of claims 1 to 3, wherein the total amount of other components, if present, is from 0 to 2% by weight.

20. A composition as claimed in any one of claims 1 to 3, wherein the total amount of other components, if present, is from 0 to 1% by weight.